Scan your signature.
Vectorise the scanned image.
Create a new document in Flash.
Import the vectorised image to the library.
Create a movie clip "signature_mc".
Copy the signature and paste it in the "Signature" layer.
In the above layer using the Pen tool, create a path for the pen to move.
Draw an image of a pen (feather, pencil).
Drag the movie clip of the pen to the scene, under the "Way" layer.
Convert the "Way" layer to guide.
Set the movement of the pen along the given path.
Return to the "Signature" layer.
Remove all the frames but for the last one in this layer.
Copy this frame, paste it to the preceding one and remove the unnecessary image up to the nib of the pen with the Eraser tool.
Then copy this frame and paste it to the preceding one, erasing the unnecessary image.
Apply this to all the frames including the first one.
The signature is ready.
Drag the movie clip to the scene and test it.